This object records the sysUpTime-based timestamp of when the currently-active T0 clock source was selected by the G.781 selection process, answering how long the device has been on its current timing source. It matters for distinguishing a stable, long-running clock selection from one that just switched moments ago, which is important context when correlating a timing anomaly with a recent switchover event. If this timestamp shows a very recent value right around when an admin also sees a spike in frame slips, that correlation strongly suggests the switchover itself, not an ongoing fault, caused the disturbance.